Means detecting non-rebailed print hammers to recycle the bailing means

ABSTRACT

A printer is disclosed having a number of hammers aligned along a transverse axis which hammers are in a cocked position awaiting a print signal, means for simultaneously bailing all hammers not in the cocked position into such position and electrooptical means having an optical axis parallel with the transverse axis of the hammers for detecting if any one or more of the hammers have not been cocked.

I Unlted stateS Patent 1151 3,673,955 Curtiss et al. 1 1 July 4, 197254] MEANS DETECTING NON-REBAILED 2,141,577 12/1938 Watson et al ..101/93MN PRINT HAMMERS o RECYCLE THE 2,482,420 9/1947 Keuper ..101/953,308,918 3/1967 James ..197/107 [72] Inventors: Robert H. Curtiss,Wayland; Richard 3,232,404 2/1966 Jones 9 /10 X H h geld Lammw, both f3,337,127 8/1967 Sundblom ..235/58 P Framingham, all of Mass. PrimaryExaminerRobert E. Pulfrey [73] Ass1gnee: Nortec Computer Devices, Inc.,Southboro, Assistam g Coven Mass- AttorneyDanie1 M. Rosen 22 F'] d: 122,1 7 l 1 y 9 0 57 ABSTRACT {21] Appl' SL103 A printer is disclosedhaving a number of hammers aligned along a transverse axis which hammersare in a cocked posi- [52] US. Cl. ..101/93 C, 235/58 P, 197/187 tionawaiting a print signal, means for simultaneously bailing [51] Int. Cl...B4lj 9/16 all hammers not in the cocked position into such positionand [58] Field of Search ..101/93 C, 96; 235/58 P, 60 P, electroopticalmeans having an optical axis parallel with the 235/132, 128,98, 144;197/47, 107, 187, 192 transverse axis of the hammers for detecting ifany one or more of the hammers have not been cocked. [56] ReferencesCited ALARM REACTIVATE 9 Claims, 1 Drawing Figure LOGlC P'A'TENTEDJUL41972 BAILING MOTO R REACTIVATE LOGIC SHUT DOWN ALARM ROBERT H. CURT/SSR/CHARD HOLZMA/V A TTOR/VEX MEANS DETECTING NON-REBAILED PRINT HAMMERSTO RECYCLE THE BAILING MEANS FIELD OF INVENTION This invention relatesto printers having means to detect hammers which have not been properlypositioned and more particularly to such printers having means toproperly position hammers so improperly positioned upon detection ofsuch condition.

BACKGROUND OF INVENTION High speed printers require hammers which mustbe actuated at the precise time that type is moving into the printposition. In order to assure proper actuation, the hammer must bepositioned so that it may receive the full driving force and impact thepaper with proper velocity at the proper time.

Commonly, hammers are driven by electromagnetic means. To reduce thepower necessary to drive the hammers, some printers employ hammers whichare mechanically bailed and held in the cocked position obtaining thedrive force by springs which are under tension when the hammers arecocked. When the hammers are released the stored energy in the cockedspring either aids the electromagnetic drive or has sufiicient'energy initself to drive the hammers to impact. In any case it is important thatthe hammers be precisely positioned prior to application of drive orrelease pulses.

No apparatus or method exists in the prior art for detecting thathammers are improperly positioned.

SUMMARY OF INVENTION It is an object of this invention to provide aprinter which as sures that print hammers are properly positioned beforethey are driven to impact the print medium.

It is a further object of this invention to provide a printer whichassures thatno data is lost due to improper hammer positioning.

It is a further object of this invention to provide a printer whichassures that drive forces are properly applied to the hammers so thatmisregistration smudging or multiple impact of the printer charactersdoes not occur.

It is a further object of this invention to provide such a printerutilizing a fail safe system.

'The invention may be accomplished by optical detecting apparatuspositioned along the line of print hammers just forward of the hammerfaces when in their preprint position. If radiation from an emittingsource is blocked by a hammer and not received at the other end of theline of hammers one or more hammers are improperly positioned.

DISCLOSURE OF PREFERRED EMBODIMENT Other objects, features andadvantAges will occur from the following description of a preferredembodiment and the accompanying drawing, which is an isometric cutawayview of the optical and mechanical portions of the invention and a blockdiagram of the electrical portions of the invention.

Each hammer 11 contains an arm .13 supported by two reed springs 15 in asuitable base or frame 17. A flat striking face 19 impacts one of: theprint medium; ribbon; or type carrier (not shown), compressing themtogether to cause printing.

The hammers 11 are shown in a rest position. A bailing arm 21 is drivencounter-clockwise about shaft 23 by bailing motor 25 to cause bail bar27 which extends the length of all the anus 13 to contact the bottomsurface of arms 13 to push them against magnetic pole pieces 29. Thehammers are held in the cocked position by the magnetic field emanatingfrom pole pieces 29. Bailing bar 27 is returned to the position shown.When printing is required, coil 31 on pole piece 29 receives a pulse ofelectrical energy over leads 33 sufficient to counteract the holdingforce of the pole piece 29 and the hammer is released from the cockedposition to an impact or print position forward of the rest positionshown. The released hammer arm 13 rebounds from the print position, issuitably damped by means (not shown) and returns to the rest position.After a print cycle is completed, hammers that are released during thatcycle are rebailed.

During the bailing process some hammers may not be cocked. To assurethat all hammers are cocked, an electro-optical system is placed alongan optical axis 35 parallel to the transverse axis of the hammers 11just forward of the location of striking faces 19 when the arms 13 arein the cocked position. The electro-optical system includes a lightemitting diode 37 having a lead 39 from its anode and a lead 41 from itscathode connected to the printer logic circuitry 43, a collimating lens45 is placed proximate to the diode 37 and a photosensitive transistor49 having emitter and collector leads, 53 and 55, connected to the logiccircuitry 43, is placed at the other end of the line of hammer arms 13.In the position shown hammer arms are not in the cocked position andradiation emitting from the diode 37 and passing through lens 45, isblocked by a portion of hammer arm 13. If all arms 13 are properlycocked, radiation from diode 37 impinges upon the base of the transistor49. The diode 37 is activated by a short pulse immediately followingcompletion of each bailing cycle. If radiation is received by transistor49, a signal is transmitted to logic 43 and the printer is free to enterthe next phase of operation. If, however, the transistor 49 does notreceive radiation during this interval either (a) one or more hammerarms 13 are not in the cocked position or (b) one of the diode 37,transistor 49 or logic 43 has failed. In any of the foregoing, theeffect is one produced by no signal received by logic 43. If any ofthese conditions occur, the logic 43 reactivates the bailing motor 25 tocock these hammer arms 13 which are blocking the transmitted light.Following the completion of the rebailing cycle, the diode 37 is againpulsed to determine if all hammers are in the cocked position. Therebailing cycle may continue N times where N is any positive integerbetween zero and a high value dependent upon the particular logic 43employed. Following the last ineffective bailing cycle the logic 43emits a signal over lead 46 to an alarm 47 which notifies an operatorthat a failureexists. The signal over lead 46 also shuts down theprinter, awaiting attention from an operator. Shut down is generally nota complete loss of power since any data stored in the printer might belost if all power were removed,

but merely a cessation of printing. The logic 43 may consist of anysuitable response mechanism for accomplishing the foregoing functions.For example, the logic may comprise a plurality of relays which willrespond to the radiation signal for activating the bailing motor 25 andthe alarm 47, as well as energizing the diode 37 in response to the endof a bailing cycle. Other modes of operation will be apparent to thoseskilled in the art, and the actual construction of such logic is notpart of the invention.

It should be noted that shut down may occur after the initial bailingcycle or after any number of rebailing cycles.

The electro-optical system is only activated for a short periodfollowing a bailing or rebailing cycle. Therefore the life of the systemis enhanced. The system is a fail safe system since any failure in theelectro-optical system will cause the lack of a proper signal to logic43 and will cause the alarm 47 to be activated.

Typical elements that may be used in the electro-optical system are:Gallium Arsenide High Efi'rciency Emitting Diode available from theRadio Corporation of America, identification number 40736R, which diodeemits infra-red radiation; Double Convex Lens available from EdmundScientific Co.; and NPN Silicon Photo Transistor available from MotorolaCorporation, identification number MRD 450.

Although the invention has been described in an embodiment with hammershaving a rest, cocked and impact position, the invention is equallyapplicable to any printer where the hammers must be in a particularposition prior to impact.

Other embodiments will occur to those skilled in the an and are withinthe following claims:

What is claimed is:

l A printer having a print cycle and a bailing cycle, comprising aplurality of print hammers each individually actuatable during a printcycle from a first to a second position for printing, repositioningmeans engageable with each of said hammers for repositioning saidhammers from said second position to said first position during abailing cycle, optical generating means providing an optical beam alongan optical path along an axis intersecting a print hammer in said secondposition, detecting means positioned in said axis for detecting anabsence of said optical beam after a bailing cycle indicating a hammerpresent in said second position after a bailing cycle and meansresponsive to the detection by said detecting means of said absence ofsaid beam for reactivating said repositioning means.

2. The printer of claim 1 wherein said detecting means is coupled tomeans for deactivating said printer if any one of said hammers is not insaid first position after a bailing cycle.

3 The printer of claim 2 wherein said detecting means is coupled tomeans for reactivating said means for repositioning if any one of saidhammers is not in said first position after a bailing cycle and saiddetecting means is coupled to said deactivating means for deactivatingsaid printer after said moving means has been reactivated N times, whereN is any positive integer.

4. The printer of claim 7 wherein said optical generating means includesa source of radiation and said detecting means an electro-opticaltransducer to receive said radiation whereby said radiation is blockedby at least one of said hammers which is not in said first position.

5. The printer of claim 4 wherein a collimating lens is placed alongsaid optical path between said source and said trans-

2. The printer of claim 1 wherein said detecting means is coupled tomeans for deactivating said printer if any one of said hammers is not insaid first position after a bailing cycle. 3 The printer of claim 2wherein said detecting means is coupled to means for reactivating saidmeans for repositioning if any one of said hammers is not in said firstposition after a bailing cycle and said detecting means is coupled tosaid deactivating means for deactivating said printer after said movingmeans has been reactivated N times, where N is any positive integer. 4.The printer of claim 7 wherein said optical generating means includes asource of radiation and said detecting means an electro-opticaltransducer to receive said radiation whereby said radiation is blockedby at least one of said hammers which is not in said first position. 5.The printer of claim 4 wherein a collimating lens is placed along saidoptical path between said source and said transducer proximate to saidsource.
 6. The device of claim 5 wherein said source of radiation is alight emitting diode and said transducer is a photo cell.
 7. The printerof claim 10 wherein said optical generating means is momentarily gatedon after activation and reactivation of said means for repositioning. 8.The printer of claim 7 wherein said first position of said hammers is acocked position.
 9. The printer of claim 8 wherein said second positionis a rest position.